Add a FailoverChannel wrapper on top of IsolationChannel to maintain a set of primary and failover channel. by parveensania · Pull Request #37840 · apache/beam

parveensania · 2026-03-12T21:26:40Z

Adds a FailoverChannel wrapper class on top of IsolationChannels to maintain primary channel and failover channel and fallback to failover channel if connectivity over primary channel cannot be established. The primary channel will again be retried after a period.

… and fallback channel

gemini-code-assist · 2026-03-12T21:27:05Z

Summary of Changes

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This pull request significantly improves the robustness of gRPC communication within Dataflow workers by implementing a failover mechanism for channels. It allows the system to gracefully handle primary channel connectivity issues by switching to a fallback channel and periodically attempting to restore the primary connection, thereby enhancing the overall stability and reliability of the worker's interaction with the Windmill service.

Highlights

New FailoverChannel Implementation: Introduced a new FailoverChannel class that wraps a primary and a fallback gRPC ManagedChannel, enabling automatic failover to the fallback channel if the primary becomes unavailable.
Resilient Channel Management: The FailoverChannel includes logic to retry the primary channel after a configurable cooling period (1 hour), enhancing the resilience of gRPC communication.
Integration into StreamingDataflowWorker: Modified StreamingDataflowWorker to conditionally create and use the FailoverChannel within the ChannelCache if isolated channels are enabled, leveraging dispatcher endpoints for fallback.
gRPC Request Enhancements: Updated the GetWorkRequest proto definition to include computation_id_filter and backend_worker_token fields, and integrated the backend_worker_token into the FanOutStreamingEngineWorkerHarness.
Testing and Utilities: Added comprehensive unit tests for FailoverChannel and refactored common test utility classes like NoopClientCall into a dedicated file for better organization.

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Changelog

runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/StreamingDataflowWorker.java
- Imported new classes for failover channel and credentials.
- Modified createChannelCache to accept GrpcDispatcherClient and to construct a FailoverChannel when isolated channels are enabled, using primary and fallback IsolationChannel instances.
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/streaming/harness/FanOutStreamingEngineWorkerHarness.java
- Updated createAndStartWindmillStreamSender to include backendWorkerToken in the GetWorkRequest if available from the endpoint.
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/windmill/client/grpc/GrpcDispatcherClient.java
- Changed the visibility of getDispatcherEndpoints() method from package-private to public.
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/windmill/client/grpc/stubs/FailoverChannel.java
- Added a new FailoverChannel class that implements ManagedChannel and provides failover logic between a primary and a fallback channel, with a cooling period for retrying the primary.
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/streaming/harness/FanOutStreamingEngineWorkerHarnessTest.java
- Modified getWorkRequest helper to accept a backendWorkerToken parameter.
- Updated testStreamsStartCorrectly to verify createDirectGetWorkStream calls with specific worker tokens.
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/windmill/client/grpc/stubs/FailoverChannelTest.java
- Added a new test class FailoverChannelTest to verify the failover and retry mechanisms of the FailoverChannel, including credential handling.
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/windmill/client/grpc/stubs/IsolationChannelTest.java
- Removed the NoopClientCall and NoopClientCallListener inner classes, as they were moved to a dedicated file.
- Changed NoopMarshaller to be public.
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/windmill/client/grpc/stubs/NoopClientCall.java
- Added a new NoopClientCall class and its inner NoopClientCallListener for use in gRPC client testing.
runners/google-cloud-dataflow-java/worker/windmill/src/main/proto/windmill.proto
- Added computation_id_filter and backend_worker_token fields to the GetWorkRequest message.

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parveensania · 2026-03-12T21:35:54Z

R: @arunpandianp

parveensania · 2026-03-12T21:36:46Z

R: @scwhittle

github-actions · 2026-03-12T21:37:13Z

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parveensania · 2026-03-12T21:42:01Z

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parveensania · 2026-03-12T21:49:49Z

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parveensania · 2026-03-12T21:50:11Z

R: @arunpandianp @scwhittle

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...va/worker/src/main/java/org/apache/beam/runners/dataflow/worker/StreamingDataflowWorker.java

…to failover-channel

arunpandianp · 2026-03-16T08:10:43Z

When looking for similar implementations, I came across GcpMultiEndpointChannel https://github.com/GoogleCloudPlatform/grpc-gcp-java/blob/master/grpc-gcp/src/main/java/com/google/cloud/grpc/GcpMultiEndpointChannel.java

GcpMultiEndpointChannel uses the channel ConnectivityStatus to determine which channel to use. Will it be more robust, if FailoverChannel uses ConnectivityStatus instead if RPC status to failover?

Thinking something like wait X seconds for primary to become ready the first time and failover to the fallback channel if it takes more than X minutes. We can let primary retry connections in the background and switch to it whenever it becomes ready.

arunpandianp · 2026-03-16T08:19:37Z

...java/org/apache/beam/runners/dataflow/worker/windmill/client/grpc/stubs/FailoverChannel.java

+  }
+
+  private void notifyFailure(Status status, boolean isFallback, String methodName) {
+    if (!status.isOk() && !isFallback && fallback != null) {


The javadoc on the class says we fallback only on UNAVAILABLE errors. Based on the code here it looks like we'll fallback on any errors. Is this expected?

https://grpc.io/docs/guides/error/ says network level issues may return UNAVAILABLE or
UNKNOWN or DEADLINE_EXCEEDED. should we include them here?

Add a wrapper on top of IsolationChannel to maintain a set of primary…

848f343

… and fallback channel

github-actions bot added runners dataflow labels Mar 12, 2026

Merge branch 'master' into failover-channel

234a533

github-actions bot added the Next Action: Reviewers label Mar 12, 2026

arunpandianp reviewed Mar 13, 2026

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...va/worker/src/main/java/org/apache/beam/runners/dataflow/worker/StreamingDataflowWorker.java Outdated Show resolved Hide resolved

parveensania added 2 commits March 16, 2026 03:11

Removing check to verify isolation channel option is set

42ec76c

Merge branch 'failover-channel' of github.com:parveensania/beam-dp in…

b64de5c

…to failover-channel

arunpandianp reviewed Mar 16, 2026

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Add a FailoverChannel wrapper on top of IsolationChannel to maintain a set of primary and failover channel.#37840

Add a FailoverChannel wrapper on top of IsolationChannel to maintain a set of primary and failover channel.#37840
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